Questioning mantle plumes

Abstract

Upon reading “Looking for mantle plumes” by Eugene Humphreys and Brandon Schmandt (PHYSICS TODAY, August 2011, page 34), I had a déjà vu moment. The first part was very familiar. It is based on laboratory fluidinjection experiments of the 1980s, the 1988 Cambridge thin-plate-geotherm model, and geochemical papers of the time. 1 (The 1988 model has been abandoned by Cambridge seismologists and is not supported by data or by realistic simulations.) Thermodynamics, selfcompression (gravity), secular cooling, radioactivity, and contemporaneous geophysics were ignored, as noted at the time. 2 The model favored in the 1980s required a homogeneous, unheated, adiabatic, melt-free upper mantle and a primordial gas-rich lower mantle and relied on simulations that were unscaled for size, pressure, and gravity. Plate-tectonic and upper- mantle boundary-layer mechanisms were discounted ab initio. Physics, which fundamentally rules out narrow upwellings in an internally heated Earth-size planet, was not a consideration, as is apparent in the figures of the PHYSICS TODAY article.